The present invention relates to a protective device for widening and enlarging the effective active surface for probes or instruments used in logging measurements and methods using this device.
The present invention allows logging measurements to be made in a large diameter well using a logging probe adapted for operation in small diameter holes.
Of course, the notion of large diameter of the hole is to be considered relatively to the dimensions of the probe.
Furthermore, the present invention protects the probes or instruments or the sensitive parts thereof against the lateral and/or longitudinal mechanical actions.
When measurements are made, because of jamming, cave-ins in the well or high thrust forces (several tens of tons even hundreds of tons) or torsional stresses communicated to the drill pipe string, the probes and/or the tools are subjected to actions likely to destroy them irremediably particularly some of these instruments which are generally very expensive.
The probes generally used in well logging have standard diameters (for example 85 mm or 92.5 mm).
These probes allow measurements of good quality to be made in holes having diameters not exceeding a maximum value. Thus, for probes measuring the resistivity of the geological formation, the ratio between the diameter of the hole and the diameter of the probe should not exceed substantially 3.5. This is due to the phenomenon called "hole effect" by a man skilled in the art and will be explained hereinafter.
By applying a device of this invention to the probe, the present invention allows good quality measurements to be made with a small diameter probe. It becomes then possible, in accordance with the present invention, to increase the range of well dimensions in which a given probe may be used.